Conventionally, for example in vegetation planting work with the object of preserving a slope and stabilizing greenery on the slope, a net made of wire netting or synthetic resin material has been set on the slope to prevent sliding of earth and sand and then planting materials such as seeds and topsoil have been blown onto the net. However, with this planting method, when due to wind and rain the planting material has been easily washed away or scattered or has slid away together with earth, the plants have not completely adhered and the objective of establishing greenery has not been achieved.
For this reason, recently, vegetation nets wherein braid parts forming meshes are of a three-dimensional structure such as a wall shape have been proposed (for example in Japanese Unexamined Patent Publication No. H.3-183820). However, in the case of this kind of net, in addition to the fact that the larger the size of the meshes (mesh openings) is made the smaller the effect of preventing earth and sand sliding becomes, there have been problems of poor shape retention of the three-dimensional braid parts, deformation such as bending and collapsing has occurred, the meshes have spread excessively and bulging of the net has occurred, and consequently problems of unsatisfactory earth and sand sliding prevention and vegetation material holding effect have arisen.
When on the other hand the meshes are made too small, in addition to the fact that the net actually obstructs the adhering and rearing of plants, the amount of yarn used increases and the net itself becomes heavy and difficult to handle and also becomes expensive.
Also, in the case of a three-dimensional net knitted with a warp knitting machine such as a double Raschel machine from front and rear base nets and connecting yarns connecting together the two base nets, whereas it is usual to use a relatively soft and extendable monofilament yarn, in some applications such as vegetation netting and cushion materials, relatively hard netting having good shape stability is required.
For example in a vegetation net, as the connecting yarns, which hold the three-dimensional shape of the net, a relatively hard thread having good shape holding is required, and from the point of view of the net setting work it is preferable that the whole net be quite hard and have good shape retention. On the other hand, from the point of view of ease of handling and carrying, a rather flexible net is preferable and it is not desirable that the whole net be made hard.
It is therefore an object of the invention to provide a three-dimensional net which as a result of comprising a net of a small mesh size has good retention of its three-dimensional structure and net shape and is strong and can well maintain characteristics resulting from its three-dimensional structure such as bulging of the net being prevented and furthermore is light and easy to handle and easy to set and can be suitably used as vegetation netting and in various other applications, and particularly to provide a net which when used as a vegetation net or a protecting net for a slope has a superior effect of preventing earth and sand sliding and preventing the runoff and scattering of vegetation material.
Another object of the invention is to provide a net the shape retention of parts forming net mesh spaces of which as a three-dimensional net is good and whose air permeability and water permeability and water retention are excellent, and also to provide a three-dimensional net which by being combined with other materials such as wadding or being combined with sheet materials can be given functions not had by conventional nets.
Further object of the invention is to provide a vegetation planting method for planting vegetation on a slope or the like in which method above-described three-dimensional net are used.